Vehicles sold in North America are required to adsorb refueling, diurnal and running loss vapors into a carbon canister. When the canister is loaded with fuel vapor, the contents may be purged to engine intake using engine intake vacuum to draw fresh air though the canister, desorbing bound hydrocarbons. Strict regulations regulate the performance of evaporative emissions systems.
In a typical canister purge operation, a canister purge valve coupled between the engine intake and the fuel canister is opened, allowing for intake manifold vacuum to be applied to the fuel canister. Simultaneously, a canister vent valve coupled between the fuel canister and atmosphere is opened, allowing for fresh air to enter the canister. This configuration facilitates desorption of stored fuel vapors from the adsorbent material in the canister, regenerating the adsorbent material for further fuel vapor adsorption.
Hybrid vehicles, and other vehicles configured to operate with minimal or no intake vacuum may have limited opportunities to purge the fuel vapor canister. Even in standard engine vehicles, the fuel vapor canister may not be completely cleared of contents following a purge, as the airflow through the canister is not uniform. If the vehicle is parked in a hot or sunny location over a diurnal cycle, the retained hydrocarbons may desorb from the canister and result in bleed emissions.
Bleed emissions may be limited by adding a secondary “bleed” canister to capture desorbed hydrocarbons. However, this adds additional cost, weight, and packaging to the vehicle. Further, in hybrid vehicles, a highly restrictive bleed canister may impede fuel tank depressurization prior to a refueling sequence, and/or may impede refueling efforts due to pressure buildup during refueling resulting in premature shutoffs of the refueling pump.
US patent application U.S. Pat. No. 9,050,885 teaches managing bleed emissions in plug-in hybrid electric vehicles. In one example, during engine-off conditions with the plug-in hybrid electric vehicle coupled to an external power source, the fuel vapor canister is cooled based on ambient temperature. For example, the canister may be cooled by activating cooling fans, and/or by circulating coolant or refrigerant through a circuit coupled to the fuel vapor canister. During conditions where ambient temperature is high, cooling the canister may reduce bleed emissions resulting from an increase in fuel vapor canister temperature. However, the inventors herein have recognized potential issues with such systems. As one example, the method is specific to plug-in hybrid electric vehicles, as cooling the canister in vehicles that are not coupled to an external power supply is not desirable due to the battery power necessary to conduct such an operation. As such, other systems and methods are desired wherein bleed emissions may be reduced without the use of costly secondary bleed canisters that may add cost and weight to the vehicle, and which may impede refueling efforts.
Thus, the inventors have herein developed systems and methods to at least partially address the above issues. In one example, a method is provided, comprising coupling a fuel tank that supplies fuel to an engine to an intake manifold of the engine during engine-off conditions, wherein an engine-off condition includes one or more of a key-off event, or a condition wherein the vehicle is powered solely by energy provided by an onboard energy storage device.
As one example, the method includes adsorbing fuel tank vapors in a fuel vapor canister positioned in an evaporative emissions system of the vehicle, and wherein coupling the fuel tank to the intake manifold during engine-off conditions routes fuel tank vapors to the fuel vapor canister to be adsorbed therein, prior to being routed to the intake manifold. In one example, the method further includes adsorbing fuel tank vapors in an adsorbent material positioned in the engine intake manifold, and wherein coupling the fuel tank to the intake manifold during engine-off conditions reduces bleed emissions from the fuel vapor canister. In this way, by coupling the fuel tank to the intake manifold during engine-off conditions, bleed emissions may be reduced, without the use of a second bleed canister that adds cost and weight to the vehicle, and which may impede refueling efforts.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.